Typical advice given writers is not to use the passive voice. What makes such advice problematic is that most of the people giving that advice generally fail to recognize the passive voice.

The most common misconception is that the passive voice involves all forms of the verb to be. Actually, it's rather depressing seeing how often such statements are made by writers, editors, and agents.

The passive voice refers to a sentence in which the subject receives the action, whereas the active voice refers to a sentence in which the subject does the action.

To be the recipient of an action doesn't necessarily mean that a sentence is weak or unworthy. For example,

Jack was murdered.

The above is in the passive voice, and I consider it among the more dynamic three-word sentences. Not only that, but it would be difficult to rephrase in the active voice and keep the sentence interesting. For example,

A party or parties unknown murdered Jack.

The sentence is in the active voice, and it is dull. In any given situation, the passive voice isn't necessarily worse nor the active voice necessarily better. More important, in terms of writing, the key question is, How important is your subject?

Of course, it is easy to go wrong with the passive voice. For example,

The door was opened by Jill when . . .

The above is passive and weak (unless one is really focused on doors). The simplest usage of the active voice is better:

Jill opened the door when . . .

For the given sentence, adding a gerund would help suggest an action leading into another action:

Jill was opening the door when . . .

Note that both the passive (The door was opened . . .) and the active (Jill was opening . . .) feature the verb to be. It leads to a somewhat simple rule: The passive is formed by the past tense of the verb to be plus the past tense of a helper verb. Combining the verb to be and a gerund maintains the active voice. For that matter, the past tense of the verb to be by itself is also in the active voice:

Jerry was in the kitchen.

All my examples feature simple sentences; it can become much more complex; but the structure is the same.

To conclude, fearing the passive voice because it is the passive voice is silly. The passive voice can be used with dramatic effect, especially for suggesting an element of mystery. In terms of number, most sentences of anyone's writing will be in the active voice, but the passive - at the right moment - can give a little something extra.

To denigrate the passive voice because of the word passive makes as much (or as little) sense as recommending perfect tenses for perfect writing.